WO2014059204A1 - Module de cellule solaire doté d'une couche d'encapsulation nanoremplie - Google Patents

Module de cellule solaire doté d'une couche d'encapsulation nanoremplie Download PDF

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Publication number
WO2014059204A1
WO2014059204A1 PCT/US2013/064425 US2013064425W WO2014059204A1 WO 2014059204 A1 WO2014059204 A1 WO 2014059204A1 US 2013064425 W US2013064425 W US 2013064425W WO 2014059204 A1 WO2014059204 A1 WO 2014059204A1
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solar cell
ionomer
layer
carboxylic acid
sheet
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PCT/US2013/064425
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English (en)
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Sam Louis Samuels
Gordon Mark Cohen
Mark David Wetzel
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E. I. Du Pont De Nemours And Company
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Priority claimed from PCT/US2013/064207 external-priority patent/WO2014059067A1/fr
Application filed by E. I. Du Pont De Nemours And Company filed Critical E. I. Du Pont De Nemours And Company
Priority to US14/430,579 priority Critical patent/US20150255653A1/en
Publication of WO2014059204A1 publication Critical patent/WO2014059204A1/fr

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/042—PV modules or arrays of single PV cells
    • H01L31/048—Encapsulation of modules
    • H01L31/0481—Encapsulation of modules characterised by the composition of the encapsulation material
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/34—Silicon-containing compounds
    • C08K3/346—Clay
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/34—Silicon-containing compounds
    • C08K3/36—Silica
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K7/00—Use of ingredients characterised by shape
    • C08K7/02—Fibres or whiskers
    • C08K7/04—Fibres or whiskers inorganic
    • C08K7/06—Elements
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
    • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
    • C08L23/04—Homopolymers or copolymers of ethene
    • C08L23/08—Copolymers of ethene
    • C08L23/0846—Copolymers of ethene with unsaturated hydrocarbons containing other atoms than carbon or hydrogen atoms
    • C08L23/0869—Acids or derivatives thereof
    • C08L23/0876—Neutralised polymers, i.e. ionomers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K2201/00—Specific properties of additives
    • C08K2201/011—Nanostructured additives
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L2205/00—Polymer mixtures characterised by other features
    • C08L2205/02—Polymer mixtures characterised by other features containing two or more polymers of the same C08L -group
    • C08L2205/025—Polymer mixtures characterised by other features containing two or more polymers of the same C08L -group containing two or more polymers of the same hierarchy C08L, and differing only in parameters such as density, comonomer content, molecular weight, structure
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy

Definitions

  • the present invention is directed to solar cell modules having encapsulant sheet layers that exhibit a low degree of creep or heat deformation.
  • the present invention relates to solar cell modules comprising an encapsulant sheet.
  • the encapsulant sheet comprises at least one layer of a composition comprising an ionomer and nano filler.
  • Solar cells can typically be categorized into two types based on the light absorbing material used, i.e., bulk or wafer-based solar cells and thin film solar cells.
  • Monocrystalline silicon (c-Si), poly- or multi- crystalline silicon (poly-Si or mc-Si) and ribbon silicon are the materials used most commonly in forming traditional wafer-based solar cells.
  • Solar cell modules derived from wafer-based solar cells often comprise a series of self- supporting wafers (or cells) that are soldered together. The wafers generally have a thickness of between about 180 and about 240 ⁇ .
  • Such a panel of solar cells is called a solar cell layer and it may further comprise electrical wirings such as cross ribbons connecting the individual cell units and bus bars having one end connected to the cells and the other exiting the module.
  • a solar cell module derived from wafer-based solar cell(s) comprises, in order of position from the front light-receiving side to the back non-light-receiving side: (1) an incident layer, (2) a front encapsulant layer, (3) a solar cell layer, (4) a back encapsulant layer, and (5) a backing layer.
  • thin film solar cells are commonly formed from materials that include amorphous silicon (a-Si), microcrystalline silicon ⁇ c-Si), cadmium telluride (CdTe), copper indium selenide (CuInSe 2 or CIS), copper indium/gallium diselenide (CuIn x Ga ( i_ X) Se 2 or CIGS), light absorbing dyes, and organic semiconductors.
  • a-Si amorphous silicon
  • microcrystalline silicon ⁇ c-Si microcrystalline silicon ⁇ c-Si
  • CdTe copper indium selenide
  • CuInSe 2 or CIS copper indium/gallium diselenide
  • light absorbing dyes and organic semiconductors.
  • thin film solar cells are disclosed in U.S. Patents 5,507,881; 5,512,107; 5,948,176; 5,994,163; 6,040,521; 6,137,048; and 6,258,620 and U.S. Patent Publications 20070298590; 200702810
  • Thin film solar cells with a typical thickness of less than 2 ⁇ are produced by depositing the semiconductor layers onto a superstate or substrate formed of glass or a flexible film. During manufacture, it is common to include a laser scribing sequence that enables the adjacent cells to be directly interconnected in series, with no need for further solder connections between cells. As with wafer cells, the solar cell layer may further comprise electrical wirings such as cross ribbons and bus bars. Similarly, the thin film solar cells are further laminated to other encapsulant and protective layers to produce a weather resistant and environmentally robust module.
  • a solar cell module derived from thin film solar cells may have one of two types of construction.
  • the first type includes, in order of position from the front light- receiving side to the back non-light-receiving side, (1) a solar cell layer comprising a superstate and a layer of thin film solar cell(s) deposited thereon at the non-light-receiving side, (2) a (back) encapsulant layer, and (3) a backing layer.
  • the second type includes, in order of position from the front light-receiving side to the back non-light-receiving side, (1) an incident layer, (2) a (front) encapsulant layer, (3) a solar cell layer comprising a layer of thin film solar cell(s) deposited on a substrate at the light-receiving side thereof, and, optionally, (4) an additional (back) encapsulant layer and (5) a backing layer.
  • the encapsulant layers used in solar cell modules are designed to encapsulate and protect the fragile solar cells.
  • Suitable polymer materials for solar cell encapsulant layers typically possess a combination of characteristics such as high impact resistance, high penetration resistance, good ultraviolet (UV) light resistance, good long term thermal stability, adequate adhesion strength to glass and other rigid polymeric sheets, high moisture resistance, and good long term weatherability.
  • the front encapsulant layers should be transparent enough to allow sunlight to effectively reach the solar cells, so that the solar cells generate the highest power output possible.
  • the polymer materials utilized in the front encapsulant layers exhibit a combination of low haze and high clarity.
  • encapsulant materials e.g., EVA, silicone
  • EVA e.g., silicone
  • Thermoplastic materials are not crosslinked and must flow at lamination temperatures (typically greater than 130°C), which has led to a concern that flow could also occur in a solar cell module under high temperature operating conditions. It is known, for example, that modules can reach peak temperatures greater than 100 °C in extreme environments.
  • thermoplastic encapsulants under high- temperature operating conditions has led to a concern about potential failures in the performance or safety of solar cell modules.
  • full module tests would be required to assure safety and module performance after exposure to such conditions, measurement of the amount of movement (creep) of a test glass laminate after exposing the glass/encapsulant/glass laminate to an elevated temperature for a specified amount of time can provide insights into relative creep performance of various materials in similar configurations, e.g. frameless glass-glass modules.
  • Ionomers are thermoplastic polymers that possess many desirable characteristics for use in solar cell encapsulant layers. Ionomers are produced by partially or fully replacing the hydrogen atoms of the acid moieties of precursor (also known as "parent") acid copolymers with ionic moieties. This is generally accomplished by neutralizing the parent acid copolymers, for example copolymers comprising copolymerized units of a-olefms and ⁇ , ⁇ -ethylenically unsaturated carboxylic acids.
  • Neutralization of the carboxylic acid groups present in such parent or precursor copolymers is generally effected by reaction of the copolymer with a base, e.g., sodium hydroxide or magnesium hydroxide, whereby the hydrogen atoms of the carboxylic acids are replaced by the cations of the base.
  • the ionomers thus formed are ionic, fully or partially neutralized polymers that comprise carboxylate groups having cations derived from reaction of the carboxylic acid with the base.
  • Ionomers are well known in the art and include polymers wherein the cations of the carboxylate groups of the ionomer are metal cations, including alkali metal cations, alkaline earth cations and transition metal cations.
  • Commercially available ionomers include those having sodium, lithium, potassium, magnesium and zinc cations.
  • ionomer compositions as interlayers in laminated safety glass is known in the art. See, e.g., U.S. Patents 3,344,014; 3,762,988; 4,663,228; 4,668,574; 4,799,346; 5,759,698; 5,763,062; 5,895,721; 6,150,028; and 6,432,522, U.S. Patent Publications 20020155302;
  • U.S. Patent 5,476,553 discloses the use, among others, of sodium ionomers such as Surlyn ® 1601 resin as an encapsulant material.
  • U.S. Patent 6,114,046 discloses a multi-layer metallocene polyolefin/ionomer laminate structure that can be used as an encapsulant.
  • ionomers including sodium and zinc ionomers, are described.
  • the invention provides solar cell module comprising a solar cell layer and a sheet comprising at least one layer of a nano filled ionomer composition, wherein (a) the solar cell layer comprises a single solar cell or a plurality of electrically interconnected solar cells; (b) the solar cell layer has a light-receiving side and a non-light-receiving side; and (c) the nanofilled ionomer composition comprises
  • a second ionomer comprising a parent acid copolymer that comprises copolymerized units of ethylene and about 18 to about 30 weight % of copolymerized units of acrylic acid or methacrylic acid, based on the total weight of the parent acid copolymer, the acid copolymer having a melt flow rate (MFR) from about 200 to about 1000 g/10 min., wherein about 50% to about 70% of the carboxylic acid groups of the copolymer, based on the total carboxylic acid content of the parent acid copolymer as calculated for the non-neutralized parent acid copolymer, are neutralized to carboxylic acid salts comprising sodium cations, potassium cations or a combination thereof; and the second ionomer has a MFR from about 1 to about 20 g/10 min. wherein MFR is measured according to ASTM D1238 at 190 °C with a 2.16 kg load.
  • the solar cell module comprises a front encapsulant layer laminated to the light-receiving side of the solar cell layer and a back encapsulant layer laminated to the non- light-receiving side of the solar cell layer, wherein at least one of the front and back encapsulant layers comprises the sheet comprising the nanofilled ionomer composition, preferably wherein a layer comprising the nanofilled ionomer composition is directly laminated to the solar cell layer.
  • the solar cell module comprises, in order of position, (i) an incident layer, (ii) a front encapsulant layer comprising the sheet comprising the nanofilled ionomer composition, and (iii) the solar cell layer, wherein the solar cell layer further comprises a substrate upon which the thin film solar cells are deposited and the substrate is positioned such that the substrate is an outermost surface of the module and is positioned on the non-light-receiving side of the solar cell layer.
  • the solar cell module comprises in order of position, (i) the solar cell layer, (ii) a back encapsulant layer comprising the sheet comprising the nanofilled ionomer composition, and (iii) a backing layer, wherein the solar cell layer further comprises a superstate upon which the thin film solar cells are deposited and the superstrate is positioned such that the superstrate is an outermost surface of the module on the light-receiving side of the solar cell layer.
  • the invention further provides a process for preparing the solar cell module described above, comprising: (i) providing an assembly comprising the solar cell layer and a sheet having at least one layer of a nanofilled ionomer composition described above; and (ii) laminating the assembly to form the solar cell module, wherein the laminating step is conducted by subjecting the assembly to heat, optionally further comprising subjecting the assembly to vacuum or pressure.
  • acid copolymer refers to a polymer comprising copolymerized units of an a-olefin, an ⁇ , ⁇ -ethylenically unsaturated carboxylic acid, and optionally, other suitable comonomer(s) such as an ⁇ , ⁇ -ethylenically unsaturated carboxylic acid ester.
  • ionomer refers to a polymer that comprises ionic groups that are metal ion carboxylates, for example, alkali metal carboxylates, alkaline earth carboxylates, transition metal carboxylates and/or mixtures of such carboxylates.
  • Such polymers are generally produced by partially or fully neutralizing the carboxylic acid groups of a precursor or "parent" polymer that is an acid copolymer, as defined herein, for example by reaction with a base.
  • an alkali metal ionomer as used herein is a sodium ionomer (or sodium neutralized ionomer), for example a copolymer of ethylene and methacrylic acid wherein all or a portion of the carboxylic acid groups of the copolymerized methacrylic acid units are in the form of sodium carboxylates.
  • nanofiller refers to inorganic materials, including without limitation solid allotropes and oxides of carbon, having a particle size of about 0.9 to about 200 nm in at least one dimension.
  • nanofilled and nanocomposite refer to a composition that contains nanofiller dispersed in a polymer matrix.
  • a nanofilled ionomer composition contains a nanofiller dispersed in a polymer matrix comprising an ionomer as defined above.
  • nanofiller in a polymer matrix, refers to a state in which the nanofiller particles are sufficiently small in size and sufficiently surrounded by the polymer matrix so that the optical clarity of the nanocomposite is not significantly compromised.
  • the nanofiller is dispersed when the haze of the nanocomposite is less than 5% and the difference in Transmitted Solar Energy (t se ) between the polymer matrix and the nanocomposite is less than 0.5%.
  • the invention provides a solar cell module comprising a) at least one layer that is a sheet comprising at least one layer of a nanofilled ionomer composition and b) a solar cell layer comprising one or a plurality of solar cells.
  • the sheet functions as an encapsulant layer in the solar cell module. That is, the solar cell modules are characterized by having an encapsulant layer having at least one layer of a nanofilled ionomer composition.
  • thermoplastic polymers The addition of certain nanoparticles to thermoplastic polymers has now been shown to significantly increase low shear viscosity and to reduce flow. It has been found that the addition of these nanoparticles to ionomers provides thermoplastic encapsulants that are "creep resistant" while maintaining transparency. Laminates comprising ionomeric interlayers that were not modified by inclusion of nano fillers deformed significantly in creep measurement tests above 100 °C, while laminates comprising nanofilled ionomer compositions as interlayers surprisingly showed little or no deformation after extended exposure to temperatures of 105 °C or 115 °C.
  • nanoclay particles are highly polar and prefer to associate with each other rather than a polymer that is of lower polarity, resulting in a poor dispersion.
  • the separated nanofiller particles that are dispersed in the ionomer as described herein do not re -agglomerate under melt processing conditions.
  • nanofilled ionomer compositions used herein contain ionomers that are ionic, neutralized derivatives of precursor acid copolymers.
  • suitable ionomers are described in U.S. Patent 7,763,360 and U.S. Patent Application Publication 2010/0112253, for example.
  • suitable precursor acid copolymers comprise copolymerized units of an a-olefin having 2 to 10 carbons and about 15 to about 25 weight % of copolymerized units of an ⁇ , ⁇ -ethylenically unsaturated carboxylic acid having 3 to 8 carbons, and 0 to about 40 weight % of other comonomers. The weight percentages are based on the total weight of the precursor acid copolymer.
  • the amount of copolymerized a-olefin is complementary to the amount of copolymerized ⁇ , ⁇ -ethylenically unsaturated carboxylic acid and of other comonomer(s), if present, so that the sum of the weight percentages of the comonomers in the precursor acid copolymer is 100%.
  • Suitable a-olefin comonomers include, but are not limited to, ethylene, propylene, 1- butene, 1-pentene, 1-hexene, 1-heptene, 3 methyl- 1-butene, 4-methyl-l-pentene, and the like and mixtures of two or more thereof.
  • the ⁇ -olefin is ethylene.
  • Suitable ⁇ , ⁇ -ethylenically unsaturated carboxylic acid comonomers include, but are not limited to, acrylic acids, methacrylic acids, itaconic acids, maleic acids, maleic anhydrides, fumaric acids, monomethyl maleic acids, and mixtures of two or more thereof.
  • the ⁇ , ⁇ -ethylenically unsaturated carboxylic acid is selected from acrylic acids, methacrylic acids, and mixtures thereof.
  • the precursor ⁇ -olefin carboxylic acid copolymer may comprise about 18 to about 25 weight %, preferably about 18 to about 23 weight %, such as about 18 to about 20 weight % or about 21 to about 23 weight %, of copolymerized units of the ⁇ , ⁇ -ethylenically unsaturated carboxylic acid and the precursor ⁇ -olefin carboxylic acid copolymer may have a melt flow rate of about 100 g/10 min or less, preferably about 30 g/10 min or less.
  • the ⁇ -olefin is ethylene.
  • the carboxylic acid is acrylic acid or methacrylic acid.
  • the precursor acid copolymers may further comprise copolymerized units of other comonomer(s), such as unsaturated carboxylic acids having 2 to 10, or preferably 3 to 8 carbons, or derivatives thereof.
  • Suitable acid derivatives include acid anhydrides, amides, and esters. Esters are preferred. Specific examples of preferred esters of unsaturated carboxylic acids include, but are not limited to, those described in U.S. Patent Application Publication 2010/0112253.
  • Examples of more preferred comonomers include, but are not limited to, alkyl (meth)acrylates such as methyl acrylate, methyl methacrylate, butyl acrylate, and butyl methacrylate; other (meth)acrylate esters, such as glycidyl methacrylate s; vinyl acetates, and mixtures of two or more thereof. Alkyl acrylates are most preferred.
  • the precursor acid copolymers may comprise 0 to about 40 weight % of other comonomers; such as about 5 to about 25 weight %. The presence of other comonomers is optional, however, and in some solar cell modules it is preferable that the precursor acid not include any other comonomer(s).
  • the precursor acid copolymers may be polymerized as disclosed in U.S. Patents 3,404,134; 5,028,674; 6,500,888; 6,518,365; 7,763,360 and U.S. Patent Application Publication 2010/0112253.
  • the precursor acid copolymers are polymerized under process conditions such that short chain and long chain branching is maximized.
  • Such processes are disclosed in, e.g., P. Ehrlich and G. A. Mortimer, "Fundamentals of Free-Radical Polymerization of Ethylene", Adv. Polymer Sci., Vol. 7, p. 386-448 (1970) and J. C. Woodley and P. Ehrlich, "The Free Radical, High Pressure Polymerization of Ethylene II.
  • the precursor acid copolymers are neutralized with for example a sodium or zinc- containing base to provide an ionomer wherein at least a portion of the hydrogen atoms of carboxyhc acid groups of the precursor acid copolymer are replaced by metal cations.
  • a sodium or zinc- containing base Preferably, about 1% to about 100%, about 5% to about 45%, about 5% to about 40%, about 10% to about 35%, or about 15% to about 30% of the hydrogen atoms of carboxyhc acid groups of the precursor acid are replaced by metal cations.
  • the acid groups are neutralized to a level of about 1% to about 100%o, or preferably about 5% to about 40%, based on the total carboxyhc acid content of the precursor acid copolymers as calculated or measured for the non-neutralized precursor acid copolymers.
  • the preferable neutralization ranges make it possible to obtain an ionomer sheet with the desirable end use properties that are novel characteristics of the compositions of the invention, such as low haze, high clarity, sufficient impact resistance and low creep, while still maintaining melt flow that is sufficiently high so that the ionomer can be processed or formed into sheets.
  • the precursor acid copolymers may be neutralized as disclosed, for example, in U.S. Patent 3,404,134.
  • melt flow rate was determined in accordance with ASTM method D1238 at 190 °C and 2.16 kg.
  • the precursor acid copolymer may have a MFR of about 0.1 g/10 min or about 0.7 g/10 min to about 30 g/10 min, about 45 g/10 min, about 55 g/10 min, or about 60 g/10 min, or about 100 g/10 min.
  • the MFR of the ionomer may be from about 0.1 to about 60 g/10 min., such as about 1.5 to about 30 g/10 min.
  • the ionomer therefrom may have a melt flow rate of about 30 g/10 min or less, preferably about 5 g/10 min or less.
  • precursor acid copolymers having a melt flow rate (MFR) of about 30 g/10 min or less. After neutralization, the MFR can be less than 5 grams/10 min, and possibly less than 2.5 g/10 min or less than 1.5 g/10 min. Suitable ionomers made by neutralizing these precursor acid copolymers with a sodium-containing base have a MFR of about 2 g/10 min or less.
  • MFR melt flow rate
  • the precursor a-olefin carboxyhc acid copolymer has a MFR of about 30 g/10 min or less;
  • the precursor ⁇ -olefin carboxyhc copolymer comprises about 21 to about 23 weight % of copolymerized units of the ⁇ , ⁇ -ethylenically unsaturated carboxyhc acid;
  • about 20% to about 35% of total content of the carboxylic acid groups present in the precursor a-olefin carboxylic have been neutralized with alkali metal ions; and
  • the ionomer has a MFR of about 5 g/10 min or less.
  • precursor acid copolymers having a melt flow rate (MFR) of about 100 g/10 min or less (such as about 60 g/10 min).
  • MFR melt flow rate
  • Suitable ionomers made by neutralizing these precursor acid copolymers with a zinc -containing base have a MFR of about 30 g/10 min or less, such as about 3 to about 27 g/10 min.
  • the precursor a-olefin carboxylic acid copolymer has a MFR of about 60 g/10 min or less;
  • the precursor a-olefin carboxylic copolymer comprises about 18 to about 20 weight % of copolymerized units of the ⁇ , ⁇ - ethylenically unsaturated carboxylic acid;
  • about 10% to about 15% of total content of the carboxylic acid groups present in the precursor ⁇ -olefin carboxylic have been neutralized with alkali metal ions; and
  • the ionomer has a MFR of about 25 g/10 min or less.
  • the ionomers may also preferably have a flexural modulus greater than about 40,000 psi (276 MPa), more preferably greater than about 50,000 psi (345 MPa), and most preferably greater than about 60,000 psi (414 MPa), as determined in accordance with ASTM method D638.
  • Water dispersable ionomers comprise or consist essentially of an ionomer derived from a parent acid copolymer that comprises copolymerized units of ethylene and about 18 to about 30 weight % of copolymerized units of acrylic acid or methacrylic acid, based on the total weight of the parent acid copolymer.
  • the parent acid copolymer has a melt flow rate (MFR) from about 200 to about 1000 g/10 min, measured according to ASTM D1238 at 190 °C with a 2160 g load.
  • the resulting water dispersable ionomer has a MFR from about 1 to about 20 g/10 min.
  • the nano filled ionomer compositions useful as polymeric sheets further contain a nanofiller.
  • the nanofiller may be present at a level of about 3 to about 70 weight %, based on the total weight of the nano filled ionomer composition, preferably from about 5 to about 20 weight %, more preferably from about 5 to about 12 weight %.
  • the nanofillers or nanomaterials suitable for use as the second component of the nano filled ionomer composition typically have a particle size of from about 0.9 to about 200 nm in at least one dimension, preferably from about 0.9 to about 100 nm.
  • the shape and aspect ratio of the nanofiller may vary, including forms such as plates, rods, or spheres.
  • the average particle size of layered silicates can be measured, for example using optical microscopy, transmission electron spectroscopy (TEM), or atomic force microscopy (AFM).
  • Preferred nanofillers for creep resistance include rodlike, platy and layered nanofillers.
  • the nanofillers may be naturally occurring or synthetic materials.
  • the nanofillers are selected from nano-sized silicas, nanoclays, and carbon nanofibers.
  • Exemplary nano-sized silicas include, but are not limited to, fumed silica, colloidal silica, fused silica, and silicates.
  • Exemplary nanoclays include, but are not limited to, smectite (e.g., aluminum silicate smectite), hectorite, fluorohectorite, montmorillonite (e.g., sodium montmorillonite, magnesium montmorillonite, and calcium montmorillonite), bentonite, beidelite, saponite, stevensite, sauconite, nontronite, and illite. Of note is sepiolite, which is rod-shaped and imparts favorable thermal and mechanical properties.
  • the carbon nanofibers used here may be single-walled nanotubes (SWNT) or multi-walled nanotubes (MWNT). Suitable carbon nanofibers are commercially available, such as those produced by Applied Sciences, Inc. (Cedarville, OH) under the tradename Pyrograf TM . Nanofillers may also be produced from hydromica or sericite.
  • a platelet filler particle (area) of a platelet filler particle divided by the thickness of the platelet.
  • Effective aspect ratio relates to the behavior of the platelet filler in a binder. Platelets in a binder may not exist in a single platelet formation. If the platelets are not in a single layer in the binder, the aspect ratio of an entire bundle, aggregate or agglomerate of platelet fillers in a binder is less than that of the individual platelet. Additional discussion of these terms may be found in U.S. Patent 6,232,389.
  • Nanofillers that are layered silicates or "phyllosilicates" are of particular note.
  • the layered silicates are obtained from micas or clays or from a combination of micas and clays.
  • Preferred layered silicates include, without limitation, pyrophillite, talc, muscovite, phlogopite, lepidolithe, zinnwaldite, margarite, hydromuscovite, hydrophlogopite, sericite, montmorillonite, nontronite, hectorite, saponite, vermiculite, sudoite, pennine, klinochlor, kaolinite, dickite, nakrite, antigorite, halloysite, allophone, palygorskite, and synthetic clays such as Laponite TM and the like that are derived from hectorite, clays that are related to hectorite, or talc.
  • the layered silicates are obtained from hectorite, fluorohectorite, pyrophillite, muscovite, phlogopite, lepidolithe, zinnwaldite, hydromuscovite, hydrophlogopite, sericite, montmorillonite, vermiculite, kaolinite, dickite, nakrite, antigorite or halloysite.
  • the layered silicates comprise materials based on or derived from hectorite, muscovite, phlogopite, pyrophyllite and zinnwaldite, for example synthetic layered silicates, hydrous sodium lithium magnesium silicates, and hydrous sodium lithium magnesium fluorosilicates based on hectorite.
  • muscovite and synthetic clays that are based on muscovite.
  • the nanofiller clays may optionally further comprise ionic fluorine, covalently bound fluorine, other cations aside from those in the natural clays, or sodium pyrophosphate.
  • More preferred layered silicates include synthetic hectorites such as LaponiteTM synthetic layered silicate, available from Rockwood Additives (Southern Clay Products, Gonzales, Texas).
  • LaponiteTM OG is a Type 2 sodium magnesium silicate with a cation exchange capacity of about 60 meq/100 g and platelets with an average size of about 83 nm long and 1 nm thick.
  • preferred synthetic hectorites such as LaponiteTM, have a particle size that is at least 50 nm in its largest dimension, or more preferably about 80 to about 100 nm.
  • the average aspect ratio of the preferred synthetic hectorites is about 80 to about 100, although aspect ratios of about 300 may also be suitable.
  • Clays, including synthetic hectorites may be characterized by their cation exchange capacity.
  • the preferred synthetic hectorites have a cation exchange capacity that is preferably less than
  • preferred synthetic hectorites have a low content of fluorine, preferably with less than 1 weight %, more preferably less than 0.1 weight %, and still more preferably less than 0.01 weight %, based on the total weight of the synthetic hectorite.
  • the surface of the layered silicates may be treated with surfactants or dispersants. Often, no such treatment is necessary or desirable.
  • the dispersant or surfactant does not comprise quaternary ammonium ions. These materials may degrade under processing conditions, lending an undesired color to the encapsulant.
  • Tetrasodium pyrophosphate (TSPP) is a notable dispersant, however.
  • the amount of the TSPP is 15 weight % or less, preferably 10 weight % or less, and more preferably 7 weight % or less, based on the total weight of the layered silicate.
  • the nanofiller particles are comminuted, disintegrated or exfoliated to thin plate-like particles by suitable methods such as calcining or milling.
  • Exfoliation is the separation of individual layers of the platelet particles and the initial close-range order within the phyllosilicates is lost in this exfoliation process.
  • the filler material used is at least partially exfoliated (at least some particles are separated into a single layer) and preferably is substantially exfoliated (the majority of the particles are separated into a single layer).
  • the neat (“dry") nanoparticles may be exfoliated, or the nanoparticles may be exfoliated in a suspension, such as a suspension in water, in another polar solvent, in oil, or in any combination of two or more suspension media.
  • the comminution, disintegration, or exfoliation may be performed by any mechanical or thermal method, or by a combination of thermal and mechanical methods, for example using a stirrer, a sonicator, a homogenizer, or a rotor-stator.
  • the nanofiller is a layered silicate that is thoroughly exfoliated (i.e., de-layered or split) to form individual nanoparticles or small aggregates of a few nanoparticles in each.
  • the layered silicates do not have any significant coloring tone. Also notable are layered silicates that do not have a coloring tone that is discernible to the naked eye and layered silicates that do not have a coloring tone that influences the color of the polymer matrix significantly.
  • the layered silicates are thoroughly comminuted, disintegrated or exfoliated from the form in which they are supplied.
  • the mean thickness of an individual platelet is about 1 nm and the mean length or width is in the range of about 25 nm to about 500 nm.
  • the mean length or width is preferably from about 40 nm to about 200 nm, and more preferably from about 75 to about 110 nm.
  • the clay particles preferably show an average aspect ratio in the range of from about 10 to about 8000, from about 30 to about 2000 or from about 50 to about 500, and more preferably the average aspect ratio is about 30 to about 150. It is preferred that the clays used in the composition be able to hydrate to form gels or sols. Transparent, colorless clays are preferred, as they minimize adverse effects on the performance of the solar modules.
  • encapsulants that are nano filled ionomeric materials will enhance the upper end-use temperature of the solar cell modules that include these encapsulants, because the nano filled ionomeric materials also have reduced creep at elevated temperatures.
  • the end-use temperature of the modules may be enhanced by up to about 20 °C to about 70 °C, or by a greater amount.
  • the encapsulants described herein have improved recyclability with respect to encapsulant materials that exhibit low creep because they have been crosslinked.
  • nanofillers will not significantly affect the optical properties of the encapsulant sheets.
  • the nanofillers effectively reduce the melt flow of the ionomer composition, while still allowing production of thermoplastic films or sheets.
  • solar cell modules having an encapsulant that comprises nanofilled ionomeric materials will be more fire resistant than solar cell modules having a conventional ionomeric encapsulant. The reason is that the nanofilled ionomeric polymers have a reduced tendency to flow out of the laminate, which in turn, could reduce the available fuel in a fire situation.
  • ionomer nanocomposites Suitable methods for the synthesis of ionomer nanocomposites are described in detail in the abovementioned concurrently filed patent application (PCT Application Serial Number PCT/US 13/64207) and in U.S. Patent 7,759,414. Briefly, however, in the field of nanocomposites, attaining a homogeneous composite, i.e., a high degree of nanoparticle dispersion within the polymer matrix, is essential for achieving target performance. It is known that certain neat nanoparticles may be added directly to a neat ionomer, then dispersed and deagglomerated, preferably using a high-shear melt mixing process.
  • a preferred concentrated nanofiller masterbatch composition comprises (a) a water dispersable ionomer (as described above) and (b) a nanofiller.
  • An aqueous dispersion of the water dispersable ionomer can be prepared by mixing the solid ionomer under low shear conditions with water heated to a temperature of from about 80 to about 90 °C. Additional information regarding suitable water dispersable ionomers and the preparation of suitable aqueous ionomer dispersions is disclosed in U.S. Application Serial Number 13/589211.
  • the aqueous ionomer dispersion can be mixed with the nanofiller, also under low shear conditions at about 80 to about 90 °C, followed by evaporation of the water to provide a solid ionomer/nano filler masterbatch.
  • the concentrated nanofiller masterbatch may comprise about 10 to about 95 weight %, about 20 to about 90 weight %, about 30 to about 90 weight %, about 40 to about 75 weight %, or about 50 to about 60 weight % of the water dispersable ionomer and about 5 to about 70 weight %, about 10 to about 70 weight %, about 20 to about 70 weight %, about 25 to about 60 weight %, or about 30 to about 50 weight % of the nanofiller, based on the total weight of the masterbatch composition.
  • One preferred method for preparing the concentrated nanofiller masterbatch is a solvent process comprising the steps of (a) dispersing nanofillers in a selected solvent such as water, optionally using a dispersant or surfactant; (b) dissolving a solid water dispersable ionomer in the same solvent system; (c) combining the solution and the dispersion; and (d) removing the solvent.
  • a solvent process comprising the steps of (a) dispersing nanofillers in a selected solvent such as water, optionally using a dispersant or surfactant; (b) dissolving a solid water dispersable ionomer in the same solvent system; (c) combining the solution and the dispersion; and (d) removing the solvent.
  • pellets or powder of a solid water dispersable ionomer and nanofiller powder are metered into the first feed port of an extruder.
  • the solid mixture is conveyed to the extruder's melting zone, where the ionomer is melted by mechanical energy input from the rotating screws and heat transfer from the barrel, and where high stresses break down the nanofiller agglomerate particles.
  • Liquid water typically deionized
  • the melted mixture is conveyed to a region of the extruder that is open to the atmosphere or under vacuum pressure, where some or all of the water evaporates or diffuses out of the mixture.
  • This evaporation or diffusion step may optionally be repeated once or more.
  • the resulting viscous polymer melt with well dispersed nanoparticles is removed from the extrudate; for example, it may be pumped by the screws and extruded through a shaping die. Should further processing under high-shear melt-mixing conditions be required to improve the dispersion quality, the extruded material may optionally be fed to the extruder and reprocessed, again optionally with water injection and removal.
  • the concentrated nanofiller masterbatch can be blended with the ionomer that forms the bulk of the polymeric matrix to produce the nanofilled ionomeric material.
  • These nanocomposite compositions may be prepared using a melt process, which includes combining all the components of the nanofilled ionomeric composition, including the masterbatch, the bulk ionomer and additional optional additives, if any. These components are melt compounded at a temperature of about 130 °C to about 230 °C, or about 170 °C to about 210 °C, to form a uniform, homogeneous blend. The process may be carried out using stirrers, Banbury TM type mixers, Brabender
  • PlastiCorder TM type mixers Haake TM type mixers, extruders, or other suitable equipment.
  • Methods for recovering the homogeneous ionomeric nanocomposite produced by melt compounding will depend on the particular piece of melt compounding apparatus utilized and may be determined by those skilled in the art. For example, if the melt compounding step takes place in a mixer such as a Brabender PlastiCorderTM mixer, the homogeneous nanocomposite may be recovered from the mixer as a single mass. If the melt compounding step takes place in an extruder, the homogeneous nanocomposite will be recovered after it exits the extruder die in a form (sheet, filament, pellets, etc.) that is determined by the shape of the die and any post- extrusion processing (such as embossing, cutting, or calendaring, e.g.) that may be applied.
  • a mixer such as a Brabender PlastiCorderTM mixer
  • the homogeneous nanocomposite may be recovered from the mixer as a single mass.
  • the melt compounding step takes place in an extruder
  • a suitable process for preparing the nanofilled ionomer composition comprises
  • dispersible ionomer as described above, with water heated to a temperature of from about 80 to about 90 °C to provide a heated aqueous ionomer dispersion;
  • Another suitable process for preparing the nanofilled ionomer composition comprises forming a concentrated nanofiller masterbatch in an extruder using water and a solid water dispersable ionomer, as described above; optionally removing the concentrated nanofiller masterbatch from the equipment, cooling it and forming it into a convenient shape, such as pellets; and melt blending the concentrated nanofiller masterbatch with another ionomer that is described above as suitable for use in the nanofilled ionomeric composition, such as the ionomer described immediately above with respect to the aqueous dispersion process.
  • a preferred nanofilled ionomer composition for use in the solar cell modules comprises:
  • an alkali metal ionomer that is an ionic, neutralized derivative of an ethylene carboxylic acid copolymer, wherein about 10% to about 35% of the total content of the carboxylic acid groups present in the precursor ethylene carboxylic acid copolymer are neutralized with alkali metal ions such as sodium, potassium or combinations thereof, and wherein the precursor ethylene carboxylic acid copolymer comprises (i) copolymerized units of ethylene and (ii) about 20 to about 25 weight %, based on the total weight of the ethylene carboxylic acid copolymer, of copolymerized units of an ⁇ , ⁇ -ethylenically unsaturated carboxylic acid having 3 to 8 carbons; having a melt flow rate (MFR) of about 2.5 g/10 min or less;
  • MFR melt flow rate
  • a second ionomer comprising a parent acid copolymer that comprises copolymerized units of ethylene and about 18 to about 30 weight % of copolymerized units of acrylic acid or methacrylic acid, based on the total weight of the parent acid copolymer, the acid copolymer having a melt flow rate (MFR) from about 200 to about 1000 g/10 min., wherein about 50% to about 70% of the carboxylic acid groups of the copolymer, based on the total carboxylic acid content of the parent acid copolymer as calculated for the non-neutralized parent acid copolymer, are neutralized to carboxylic acid salts comprising sodium cations, potassium cations or a combination thereof; and the second ionomer has a MFR from about 1 to about 20 g/10 min. measured according to ASTM D1238 at 190 °C with a 2.16 kg load.
  • MFR melt flow rate
  • Another preferred nanofilled ionomer composition for use in the solar cell modules comprises:
  • MFR melt flow rate
  • a second ionomer comprising a parent acid copolymer that comprises copolymerized units of ethylene and about 18 to about 30 weight % of copolymerized units of acrylic acid or methacrylic acid, based on the total weight of the parent acid copolymer, the acid copolymer having a melt flow rate (MFR) from about 200 to about 1000 g/10 min., wherein about 50% to about 70% of the carboxylic acid groups of the copolymer, based on the total carboxylic acid content of the parent acid copolymer as calculated for the non-neutralized parent acid copolymer, are neutralized to carboxylic acid salts comprising sodium cations, potassium cations or a combination thereof; and the second ionomer has a MFR from about 1 to about 20 g/10 min. measured according to ASTM D1238 at 190 °C with a 2.16 kg load.
  • MFR melt flow rate
  • the extent of dispersion of the nanofiller in the polymer matrix can be measured by X-ray diffraction.
  • X-ray diffraction X-ray diffraction
  • XRD X-ray diffraction
  • the interlayer spacing i.e., the distance between two adjacent clay platelets, can be determined from the peak position of the XRD pattern.
  • the interlayer spacing increases, and the reflection peak of the XRD pattern moves to a lower 2-THETA position. Under such conditions, the nanoclay is considered to be intercalated.
  • the masterbatch and the nanofilled ionomer composition may also contain other additives known in the art.
  • Suitable additives include, but are not limited to, processing aids, flow enhancing additives, lubricants, pigments, dyes, flame retardants, impact modifiers, nucleating agents, anti-blocking agents such as silica, thermal stabilizers, UV absorbers, UV stabilizers, dispersants, surfactants, chelating agents, coupling agents, reinforcement additives, such as glass fiber, fillers and the like.
  • thermal stabilizers UV absorbers, hindered amine light stabilizers (HALS), and silane coupling agents.
  • HALS hindered amine light stabilizers
  • Suitable and preferred examples of these additives and suitable and preferred levels of these additives are set forth in in U.S. Patent Application Publication 2010/0112253.
  • additives that may reduce the optical clarity of the composition such as reinforcement additives and fillers, are reserved for those sheets that are used as the back encapsulants.
  • compositions are most preferably made without use of organic peroxides, crosslinking agents or initiators (so that the sheets and the interlayers of the laminates do not contain organic peroxides and are not crosslinked).
  • the sheet that functions as one component of the solar modules described herein may be in a single layer or in multilayer form.
  • single layer it is meant that the sheet is made of or consists essentially of the nanofilled ionomer composition.
  • the other sub-layer(s) may be made of any other suitable polymeric material(s), such as, for example, acid copolymers as previously defined herein, ionomers as previously defined herein, poly(ethylene vinyl acetates), poly(vinyl acetals) (including acoustic grade poly(vinyl acetals)), polyurethanes, polyvinylchlorides, polyethylenes (e.g., linear low density polyethylene s), polyolefm block elastomers, copolymers of a-olefms and ⁇ , ⁇ -ethylenically uns
  • the total thickness of the sheet that comprises at least one layer of the nanofilled ionomer composition may be in the range of about 10 to about 90 mil (about 0.25 to about 2.3 mm), preferably about 10 to about 60 mil (about 0.25 to about 1.5 mm), more preferably about 15 to about 55 mil (about 0.38 to about 1.4 mm), yet more preferably about 15 to about 45 mil (about 0.38 to about 1.14 mm), yet more preferably about 15 to about 35 mil (about 0.38 to about 0.89 mm), and most preferably about 18 to about 35 mil (about 0.64 to about 0.89 mm).
  • the thickness of the individual sub-layers of the nanofilled encapsulant layer is not critical and may be independently varied depending on the requirements of the particular application.
  • the sheet comprising the nanofilled ionomer composition may have a smooth or rough surface on one or both sides.
  • the sheet has rough surfaces on both sides to facilitate deaeration during the lamination process.
  • Rough surfaces can be created by mechanically embossing or by melt fracture during extrusion of the sheets followed by quenching so that surface roughness is retained during handling.
  • the surface pattern can be applied to the sheet through processes that are commonly known in the art. For example, the as-extruded sheet may be passed over a specially prepared surface of a die roll positioned in close proximity to the exit of the die which imparts the desired surface characteristics to one side of the molten polymer.
  • the polymer sheet cast thereon will have a rough surface on the side that is in contact with the roll, and the rough surface generally conforms respectively to the valleys and peaks of the roll surface.
  • Such die rolls are disclosed in, e.g., U.S. Patent 4,035,549 and U.S. Patent Publication 2003/0124296.
  • the sheets comprising the nanofilled ionomer composition can be produced by any suitable process.
  • the sheets may be formed through dipcoating, solution casting, compression molding, injection molding, lamination, melt extrusion, blown film, extrusion coating, tandem extrusion coating, or by any other procedures that are known to those of skill in the art.
  • the sheets are formed by melt extrusion, melt coextrusion, melt extrusion coating, or tandem melt extrusion coating processes.
  • a solar cell module comprising at least one layer that is a sheet (i.e. encapsulant layer) comprising at least one layer of the above-described nanofilled ionomer composition and a solar cell layer comprised of one or a plurality of solar cells.
  • solar cell includes any article which can convert light into electrical energy.
  • Solar cells useful in the invention include, but are not limited to, wafer-based solar cells (e.g., c-Si or mc-Si based solar cells, as described above in the background section) and thin film solar cells (e.g., a-Si, ⁇ -Si, CdTe, or CI(G)S based solar cells, as described above in the background section).
  • wafer-based solar cells e.g., c-Si or mc-Si based solar cells, as described above in the background section
  • thin film solar cells e.g., a-Si, ⁇ -Si, CdTe, or CI(G)S based solar cells, as described above in the background section.
  • the solar cells be electrically interconnected or arranged in a flat plane.
  • the solar cell layer may further comprise electrical wirings, such as cross ribbons and bus bars.
  • the solar cell module comprises at least one layer of a sheet comprising the nanofilled ionomer composition, which is laminated to the solar cell layer and serves as an encapsulant layer.
  • laminated as used herein, for example to refer to layers within a laminated structure, refers to two layers are bonded either directly (i.e., without any additional material between the two layers) or indirectly (i.e., with additional material, such as interlayer or adhesive materials, between the two layers).
  • the sheet comprising the nanofilled ionomer composition is directly laminated or bonded to the solar cell layer.
  • the solar cell layer has a light-receiving and non- light-receiving side and which comprises a front encapsulant layer laminated to the light-receiving side of the solar cell layer and a back encapsulant layer laminated to the non-light-receiving side of the solar cell layer, wherein at least one of the front and back encapsulant layers comprises the nanofilled ionomer composition.
  • the solar cell module may further comprise additional encapsulant layers comprising other polymeric materials, such as for example acid copolymers as previously defined herein, ionomers as previously defined herein, poly(ethylene vinyl acetates), poly(vinyl acetals) (including acoustic grade poly(vinyl acetals)), polyurethanes, poly(vinyl chlorides), polyethylenes (e.g., linear low density polyethylenes), polyolefm block elastomers, copolymers of ⁇ -olefms and ⁇ , ⁇ - ethylenically unsaturated carboxylic acid esters) (e.g., ethylene methyl acrylate copolymers and ethylene butyl acrylate copolymers), silicone elastomers, epoxy resins, and combinations of two or more thereof.
  • polymeric materials such as for example acid copolymers as previously defined herein, ionomers as previously defined herein, poly(ethylene vinyl acetates), poly(
  • the thickness of the individual encapsulant layers other than the sheet(s) comprising the nanofilled ionomer composition may independently range from about 1 mil (0.026 mm) to about 120 mils (3 mm), or preferably from about 1 mil to about 40 mils (1.02 mm), or more preferably from about 1 mil to about 20 mils (0.51 mm).
  • Any or all of the encapsulant layer(s) comprised in the solar cell modules may have smooth or rough surfaces.
  • the encapsulant layer(s) have rough surfaces to facilitate deaeration during the lamination process.
  • the solar cell module may further comprise an incident layer or a backing layer serving as the outermost layer or layers of the module at the light-receiving side and the non-light- receiving side of the solar cell module, respectively.
  • the outer layers of the solar cell modules may be derived from any suitable sheets or films.
  • Suitable sheets may be glass or polymeric sheets, such as those comprising a polymer selected from polycarbonates, acrylics, polyacrylates, cyclic polyolefms (e.g., ethylene norbornene polymers), polystyrenes (preferably metallocene- catalyzed polystyrenes), polyamides, polyesters, fluoropolymers, or combinations of two or more thereof.
  • metal sheets such as aluminum, steel, galvanized steel, or ceramic plates may be utilized in forming the backing layer.
  • glass includes not only window glass, plate glass, silicate glass, sheet glass, low iron glass, tempered glass, tempered CeO-free glass, and float glass, but also colored glass, specialty glass (such as those containing ingredients to control solar heating), coated glass (such as those sputtered with metals (e.g., silver or indium tin oxide) for solar control purposes), E-glass, Toroglass, Solex ® glass (PPG Industries, Pittsburgh, PA) and Starphire ® glass (PPG Industries).
  • specialty glasses are disclosed in, e.g., U.S. Patents 4,615,989; 5,173,212; 5,264,286;
  • Suitable film layers comprise polymers that include but are not limited to, polyesters (e.g., poly(ethylene terephthalate) and poly(ethylene naphthalate)), polycarbonate, polyolefms (e.g., polypropylene, polyethylene, and cyclic polyolefms), norbornene polymers, polystyrene (e.g., syndiotactic polystyrene), styrene-acrylate copolymers, acrylonitrile-styrene copolymers, polysulfones (e.g., polyethersulfone, polysulfone, etc.), polyamides, poly(urethanes), acrylics, cellulose acetates (e.g., cellulose acetate, cellulose triacetates, etc.), cellophane, poly(vinyl chlorides) (e.g., poly(vinylidene chloride)), fluoropolymers (e.g., poly
  • the polymeric film may be bi-axially oriented polyester film (preferably poly(ethylene terephthalate) film) or a fluoropolymer film (e.g., Tedlar ® , Tefzel ® , and Teflon ® films, from E. I. du Pont de Nemours and Company, Wilmington, DE (DuPont)). Fluoropolymer-polyester-fluoropolymer (e.g., "TPT”) films are also preferred for some applications. Metal films, such as aluminum foil, may also be used as the backing layers.
  • the solar cell module may further comprise other functional film or sheet layers (e.g., dielectric layers or barrier layers) embedded within the module.
  • functional layers may be derived from any of the above mentioned polymeric films or those that are coated with additional functional coatings.
  • poly(ethylene terephthalate) films coated with a metal oxide coating such as those disclosed in U.S. Patents 6,521,825 and 6,818,819 and European Patent EP 1182710, may function as oxygen and moisture barrier layers in the laminates.
  • a layer of nonwoven glass fiber may also be included between the solar cell layers and the encapsulants to facilitate deaeration during the lamination process or to serve as reinforcement for the encapsulants.
  • the use of such scrim layers is disclosed in, e.g., U.S. Patents 5,583,057; 6,075,202; 6,204,443; 6,320,115; and 6,323,416 and European Patent EP0769818.
  • the film or sheet layers positioned to the light-receiving side of the solar cell layer are preferably made of transparent material to allow efficient transmission of sunlight into the solar cells.
  • the light-receiving side of the solar cell layer may sometimes be referred to as a front side and in actual use conditions would generally face a light source.
  • the non-light-receiving side of the solar cell layer may sometimes be referred to as a lower or back side and in actual use conditions would generally face away from a light source.
  • a special film or sheet may be included to serve both the function of an encapsulant layer and an outer layer. It is also conceivable that any of the film or sheet layers included in the module may be in the form of a pre-formed single- layer or multi-layer film or sheet.
  • Another suitable type of solar cell module is designed so that both of its sides are transparent and positioned to receive light that is transmitted to the solar cell layer.
  • one or both surfaces of the incident layer films and sheets, the backing layer films and sheets, the encapsulant layers and other layers incorporated within the solar cell module may be treated prior to the lamination process to enhance the adhesion to other laminate layers.
  • This adhesion enhancing treatment may take any form known in the art and includes those set forth in U.S. Patent Application Publication 2010/0108126.
  • the solar cell module may comprise, in order of position from the front light-receiving side to the back non-light-receiving side, (a) an incident layer, (b) a front encapsulant layer, (c) a solar cell layer comprised of one or more electrically interconnected solar cells, (d) a back encapsulant layer, and (e) a backing layer, wherein at least one or both of the front and back encapsulant layers comprises the nano filled ionomer composition comprising sheets.
  • the solar cell modules are derived from thin film solar cells and may (i) in one embodiment, comprise, in order of position from the front light-receiving side to the back non-light-receiving side, (a) a solar cell layer comprising a superstate and a layer of thin film solar cell(s) deposited thereon at the non-light-receiving side, (b) a (back) encapsulant layer comprising the nanofilled ionomer composition comprising sheet, and (c) a backing layer or (ii) in a more preferred embodiment, comprise, (a) a transparent incident layer, (b) a (front) encapsulant layer comprising the nanofilled ionomer comprising sheet, and (c) a solar cell layer comprising a layer of thin film solar cell(s) deposited on a substrate at the light-receiving side thereof.
  • a series comprising two or more of the solar cell modules described above may be further linked to form a solar cell array, which can produce a desired voltage and current.
  • the solar cell modules in the array may be the same or different.
  • any lamination process known in the art may be used to prepare the solar cell modules.
  • the component layers of the solar cell module are stacked in the desired order to form a pre-lamination assembly.
  • a vacuum bag capable of sustaining a vacuum
  • the air is drawn out of the bag by a vacuum line or other means
  • the bag is sealed while the vacuum is maintained (e.g., at least about 27 to 28 inches of Hg (689-711 mm Hg))
  • the sealed bag is placed in an autoclave at a pressure of about 150 to about 250 psi (about 11.3 to about 18.8 bar), a temperature of about 130 °C to about 180 °C, or about 120 °C to about 160 °C, or about 135 °C to about 160 °C, or about 145 °C to about 155 °C, for about 10 to about 50 min, or about 20 to about 45 min, or about 20 to about 40 min, or about 25 to about 35 min.
  • a vacuum ring may be substituted for the vacuum bag.
  • One type of suitable vacuum bag is disclosed within U.S. Patent 3,311,517. Following the heat and pressure cycle, the air in the autoclave is cooled without adding additional gas to maintain pressure in the autoclave. After about 20 min of cooling, the excess air pressure is vented and the laminates are removed from the autoclave.
  • the pre-lamination assembly may be heated in an oven at about 80 °C to about 120 °C, or about 90 °C to about 100 °C, for about 20 to about 40 min, and thereafter, the heated assembly is passed through a set of nip rolls so that the air in the void spaces between the individual layers may be squeezed out, and the edge of the assembly sealed.
  • the assembly at this stage is referred to as a pre -press.
  • the pre-press may then be placed in an air autoclave where the temperature is raised to about 120 °C to about 160 °C, or about 135 °C to about 160 °C, at a pressure of about 100 to about 300 psi (about 6.9 to about 20.7 bar), or preferably about 200 psi (13.8 bar). These conditions are maintained for about 15 to about 60 min, or about 20 to about 50 min, after which the air is cooled while no further air is introduced to the autoclave. After about 20 to about 40 min of cooling, the excess air pressure is vented and the laminated products are removed from the autoclave.
  • the solar cell modules may also be produced through non-autoclave processes.
  • non-autoclave processes are disclosed, e.g., in U.S. Patents 3,234,062; 3,852,136; 4,341,576; 4,385,951; 4,398,979; 5,536,347; 5,853,516; 6,342,116; and 5,415,909, U.S. Patent Publication 2004/0182493, European Patent EP1235683 Bl, and PCT Patent Publications WO91/01880 and WO03/057478.
  • the non-autoclave processes include heating the pre-lamination assembly and the application of vacuum, pressure or both.
  • the assembly may be successively passed through heating ovens and nip rolls.
  • Particularly useful processes include vacuum lamination using, for example, Meier or Burkle laminators. These examples of lamination processes are not intended to be limiting. Essentially any lamination process may be used.
  • the encapsulant sheets are generally supplied as sheets having a substantially uniform thickness.
  • the polymeric encapsulant sheets melt or soften to some degree.
  • the encapsulant also flows around the surface peaks or contours of the solar cell assembly.
  • the air trapped in the voids is extracted or dissolved during the vacuum or pressure stages of lamination. As is discussed above, the extraction of the trapped air is facilitated when the encapsulant has one or more roughened surfaces.
  • any voids between the solar cell assembly and the encapsulant sheets are filled during the lamination process to provide solar cell modules in which the encapsulant is in good contact with the solar cell assembly.
  • edges of the solar cell module may be sealed to reduce moisture and air intrusion and potential degradative effects on the efficiency and lifetime of the solar cell(s) by any means disclosed in the art.
  • Suitable edge seal materials include, but are not limited to, butyl rubber, polysulfide, silicone, polyurethane, polypropylene elastomers, polystyrene elastomers, block elastomers, styrene-ethylene-butylene-styrene (SEBS), and the like.
  • Ionomers The ethylene/methacrylic acid dipolymers listed in Table 1 were neutralized to the indicated extent by treatment with NaOH, zinc oxide or KOH using standard procedures to form sodium, zinc or potassium-containing ionomers. Melt flow rates (MFR) were determined in accordance with ASTM D1238 at 190 °C with a 2.16 kg mass.
  • Methacrylic acid MFR Neutralization Level MFR weight %* g/10 min Cation % g/10 min
  • ION-1 and ION-3 are ionomers that are not readily water dispersable.
  • ION-2 is a water dispersable ionomer.
  • Nano filler NF-1 a Type 2 sodium magnesium silicate with a cation exchange capacity of about 60 meq/100 g and platelets about 83 nm long and 1 nm thick, commercially available from Rockwood Additives (Southern Clay Products, Gonzales, Texas) as Laponite TM OG.
  • Additive UVS-1 a UV-stabilizer commercially available from BASF under the tradename Tinuvin TM 328.
  • Pellets of ionomer were fed into a 25 mm diameter Killion extruder using the general temperature profile set forth in Table 2.
  • the polymer throughput was controlled by adjusting the screw speed.
  • UVS-1 (0.12 weight % based on the amount of polymer) was added to ION-1 in a single screw extruder operating at about 230 °C. The resulting mixture was cast into a sheet for subsequent lamination as detailed below. The sheet measured about 0.9 mm thick.
  • a round-bottom flask equipped with a mechanical stirrer, a heating mantle, and a temperature probe associated with a temperature controller for the heating mantle was charged with water.
  • the water was stirred and the neat solid ionomer ION-2 was added to the water at room temperature.
  • the aqueous ionomer mixture was stirred at room temperature for 5 minutes and then heated to 80 °C. Next, the mixture was stirred for 20 min at 90 °C until the ionomer was fully incorporated into the water, as judged by the clarity of the mixture.
  • the heating mantle and temperature controller were removed from the round-bottom flask, and the aqueous ionomer mixture was cooled to room temperature with continued stirring.
  • Nano filler was added as a powder to the aqueous ionomer mixture. During the addition, the aqueous ionomer mixture was stirred rapidly so that the nanofiller was incorporated smoothly without forming dry lumps. Stirring was continued for approximately 30 min until the nanofiller was dispersed, again as judged by the clarity of the mixture.
  • the rotary evaporation under heat and vacuum were continued for one to two days.
  • the solid product was removed from the round bottom flask and further dried for about 16 to 64 hours in an oven at
  • lonomer A 50 °C under house vacuum (about 120 to 250 mm Hg) with a slowly flowing nitrogen atmosphere.
  • aqueous dispersion of ION-2 was prepared and dried according to the general aqueous dispersion procedure above, in quantities shown in Table 3. There was no filler in this material.
  • Ionomer B was melt-blended in the mixer with 30.0 g of ION-1. The materials were mixed at 140
  • a blend comprising ION-3 and 10 weight % of nanofiller is prepared using a similar procedure by substituting ION-3 for ION-1, blended with Ionomer B.
  • Two films were formed by molding the composition of Example 1 (see Table 4) in a hydraulic press at 215 °C, incrementally raising the pressure to 152 MPa, and holding the temperature and pressure for 210 seconds, followed by cooling to around 37 °C and removing the resultant films from the mold. Cooled films measured about 0.8 mm thick.
  • glass laminates were prepared by the Lamination Process described below, using the films of Comparative
  • Each glass/encapsulant/glass laminate comprised a 102 mm x 102 mm film of the encapsulants described above, a 102 mm x 204 mm x 3 mm (rectangular) bottom glass plate and a 102 mm x 102 mm x 3 mm (square) top glass plate and were laminated as follows.
  • the glass plates were high clarity, low iron Diamant ® float glass from Saint Gobain Glass. Pre-laminates were laid-up with the encapsulant film and the square glass plate coinciding and offset about 25mm from one of the short edges of the rectangular glass plate.
  • the glass laminates were tested for heat deformation or "creep.” Each laminate was hung from the top rack of an air oven by the 25-mm exposed edge of the larger glass plate using binder clips. The oven was preheated to 105 °C or to 115 °C. The other end of the larger glass plate rested on a catch pan to prevent the laminate from slipping out of the binder clips. With this mounting system, the rectangular glass plate was constrained in a vertical position while the encapsulant and square glass plate were unsupported and unconstrained. The vertical displacement of the smaller glass plates was measured periodically and reported in Table 5.
  • a ZSK-18mm intermeshing, co-rotating twin-screw extruder (Coperion Corporation of Ramsey, NJ) with 41 Length/Diameter (L/D) was used to make a an ION-2/NF-1 composite concentrate masterbatch using a melt extrusion process with water injection and removal.
  • a conventional screw configuration containing a solid transport zone to convey pellets and clay powder from the first feed port, a melting section consisting of a combination of kneading blocks and several reverse pumping elements to create a seal to minimize water vapor escape, a melt conveying and liquid injection region, an intensive mixing section consisting of several combinations kneading block, gear mixer and reverse pumping elements to promote dispersion, distribution and polymer dissolution and water diffusion, one melt degassing and water removal zone and a melt pumping section.
  • the melt was extruded through a die to form strands that were quenched in water at room temperature and cut into pellets.
  • Polymer pellets and solid powders were metered into the extruder separately using loss in weight feeders (KTron Corp., Pitman, NJ).
  • Deionized (de -mineralized) water was injected into the extruder downstream of the melting zone using a positive displacement pump (Teledyne ISCO 500D, Lincoln, NE). No attempt to exclude oxygen from the extruder was made.
  • One vacuum vent zone was used to extract a portion of the water, volatile gases and entrapped air. Barrel temperatures, after the unheated feed barrel section, were set in a range from 160 to 185 °C depending on heat transfer and thermal requirements for melting, liquid injection, mixing, water removal and extrusion through the die.
  • the throughput was fixed at 10 lb/hr and the screw rotational speed was 500 rpm.
  • the deionized water injection flow rate was set to approximately 30 mL/minute.
  • the extruded masterbatch pellets were then fed into the extruder for a second pass at a throughput of 10 lb/hr, a screw speed of 525 rpm, and a water injection flow rate of 16 ml/minute.
  • a masterbatch with NF-1 silicate concentration of 25 weight % was produced. No organic surface modifiers were used on the NF-1 or added during the extrusion process.
  • a ZSK-18mm intermeshing, co-rotating twin-screw extruder (Coperion Corp.) with 41 Length/Diameter (L/D) was used to melt and mix masterbatch MB2 described immediately above with ION- 1 matrix polymer.
  • a conventional screw configuration was used containing a solid transport zone to convey pellets from the first feed port, a melting section consisting of a combination of kneading blocks and one or more reverse pumping elements, a melt conveying region, a distributive mixing section consisting of several combinations of kneading block, gear mixer and reverse pumping elements, one melt degassing zone and a melt pumping section.
  • the glass laminates were thoroughly cleaned using Windex ® glass cleaner and lintless cloths to ensure that they were substantially free of dirt and other contaminants that might otherwise interfere with making valid optical measurements.
  • the transmission spectrum of each laminate was then determined using a Varian Cary 5000 UV7VIS/NIR spectrophotometer (version 1.12) equipped with a DRA-2500 diffuse reflectance accessory, scanning from 2500 nm to 200 nm, with UV-VIS data interval of 1 nm and UV-VIS-NIR scan rate of 0.200 seconds/nm, utilizing full slit height and operating in double beam mode.
  • the DRA-2500 is a 150mm integrating sphere coated with SpectralonTM.
  • Example 8 The results in Table 8 show that Comparative Example C3 exhibited significant creep during the thermal exposure. In contrast, the nanofilled compositions (Examples 2 and 3) exhibited superior creep resistance throughout the duration of the tests. Example 3, in which the ionomeric interlay er sheet contained 10 weight % of nano filler, provided excellent creep resistance.
  • Heat deflection temperature may be determined for the compositions at 264 psi (1.8 MPa) according to ASTM D648.

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  • Chemical & Material Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Organic Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Medicinal Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Electromagnetism (AREA)
  • Power Engineering (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Computer Hardware Design (AREA)
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  • Physics & Mathematics (AREA)
  • Dispersion Chemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Photovoltaic Devices (AREA)
  • Compositions Of Macromolecular Compounds (AREA)

Abstract

L'invention concerne un module de cellule solaire comprenant une couche de cellule solaire et une feuille comprenant au moins une couche d'une composition d'ionomère nanoremplie. La composition d'ionomère nanoremplie comprend (1) un ionomère issu d'un copolymère d'alpha-oléfine/acide carboxylique précurseur, et (a) le copolymère alpha-oléfine/acide carboxylique précurseur comprend (i) des unités copolymérisées d'une alpha-oléfine et (ii) environ 20 à environ 25 % en poids d'unités copolymérisées d'un acide carboxylique à insaturation éthylénique alpha, beta, et (b) au moins une partie de la teneur totale en groupes d'acide carboxylique présents dans le copolymère alpha-oléfine/acide carboxylique précurseur a été neutralisée pour former des sels métalliques de groupes d'acide carboxylique; et (2) une ou plusieurs nanocharges.
PCT/US2013/064425 2012-10-12 2013-10-11 Module de cellule solaire doté d'une couche d'encapsulation nanoremplie WO2014059204A1 (fr)

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PCT/US2013/064207 WO2014059067A1 (fr) 2012-10-12 2013-10-10 Composite ionomère

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Cited By (1)

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WO2015085165A1 (fr) 2013-12-06 2015-06-11 E. I. Du Pont De Nemours And Company Feuilles de couche intermédiaire polymères et stratifiés légers produits à partir de celles-ci

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CN107001693B (zh) * 2014-10-30 2019-05-21 陶氏环球技术有限责任公司 具有包含微粉化硅胶的膜层的光伏模块
EP3898830B1 (fr) 2018-12-20 2022-11-02 Dow Global Technologies LLC Dispersions aqueuses d'ionomères et procédés associés

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WO2011041653A2 (fr) * 2009-10-01 2011-04-07 7Solar Technologies, Inc. Matériau encapsulant pour cellules photovoltaïques
US20120024348A1 (en) * 2010-07-30 2012-02-02 E.I. Du Pont De Nemours And Company Cross-linkable ionomeric encapsulants for photovoltaic cells

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FR2896445B1 (fr) * 2006-01-25 2010-08-20 Arkema Film flexible a base de polymere fluore
US20090255571A1 (en) * 2008-04-14 2009-10-15 Bp Corporation North America Inc. Thermal Conducting Materials for Solar Panel Components
KR101623603B1 (ko) * 2008-06-02 2016-05-23 이 아이 듀폰 디 네모아 앤드 캄파니 탁도가 낮은 봉지제 층을 가진 태양 전지 모듈
CN102931260A (zh) * 2008-10-31 2013-02-13 陶氏康宁公司 光生伏打电池组件和形成方法

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WO2011041653A2 (fr) * 2009-10-01 2011-04-07 7Solar Technologies, Inc. Matériau encapsulant pour cellules photovoltaïques
US20120024348A1 (en) * 2010-07-30 2012-02-02 E.I. Du Pont De Nemours And Company Cross-linkable ionomeric encapsulants for photovoltaic cells

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2015085165A1 (fr) 2013-12-06 2015-06-11 E. I. Du Pont De Nemours And Company Feuilles de couche intermédiaire polymères et stratifiés légers produits à partir de celles-ci

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